/*                              - checksum.c -

  Simple checksum routines.

  Created 970615 by Grzm.

  (c) Copyright IAR Systems 1997-2005.

  $Id: checksum.c 1.1 1997/06/30 12:20:20 Grzm Exp $
  $Log: checksum.c $
  Revision 1.1  1997/06/30 12:20:20  Grzm
  Initial revision
  Addapted for ARM memory space 2006-01-11    IMAL
                                                                              */

/* Here's a couple of sample functions to use to calculate a checksum in
   a few different ways. Take whatever you need and modify as desired. */


static const unsigned short crc16_table[256] =
{
    0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7, 0x8108,
    0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef, 0x1231, 0x0210,
    0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6, 0x9339, 0x8318, 0xb37b,
    0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de, 0x2462, 0x3443, 0x0420, 0x1401,
    0x64e6, 0x74c7, 0x44a4, 0x5485, 0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee,
    0xf5cf, 0xc5ac, 0xd58d, 0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6,
    0x5695, 0x46b4, 0xb75b, 0xa77a, 0x9719, 0x8738, 0xf7df, 0xe7fe, 0xd79d,
    0xc7bc, 0x48c4, 0x58e5, 0x6886, 0x78a7, 0x0840, 0x1861, 0x2802, 0x3823,
    0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b, 0x5af5,
    0x4ad4, 0x7ab7, 0x6a96, 0x1a71, 0x0a50, 0x3a33, 0x2a12, 0xdbfd, 0xcbdc,
    0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a, 0x6ca6, 0x7c87, 0x4ce4,
    0x5cc5, 0x2c22, 0x3c03, 0x0c60, 0x1c41, 0xedae, 0xfd8f, 0xcdec, 0xddcd,
    0xad2a, 0xbd0b, 0x8d68, 0x9d49, 0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13,
    0x2e32, 0x1e51, 0x0e70, 0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a,
    0x9f59, 0x8f78, 0x9188, 0x81a9, 0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e,
    0xe16f, 0x1080, 0x00a1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067,
    0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e, 0x02b1,
    0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256, 0xb5ea, 0xa5cb,
    0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d, 0x34e2, 0x24c3, 0x14a0,
    0x0481, 0x7466, 0x6447, 0x5424, 0x4405, 0xa7db, 0xb7fa, 0x8799, 0x97b8,
    0xe75f, 0xf77e, 0xc71d, 0xd73c, 0x26d3, 0x36f2, 0x0691, 0x16b0, 0x6657,
    0x7676, 0x4615, 0x5634, 0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9,
    0xb98a, 0xa9ab, 0x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x08e1, 0x3882,
    0x28a3, 0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a,
    0x4a75, 0x5a54, 0x6a37, 0x7a16, 0x0af1, 0x1ad0, 0x2ab3, 0x3a92, 0xfd2e,
    0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9, 0x7c26, 0x6c07,
    0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1, 0xef1f, 0xff3e, 0xcf5d,
    0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8, 0x6e17, 0x7e36, 0x4e55, 0x5e74,
    0x2e93, 0x3eb2, 0x0ed1, 0x1ef0,
};


unsigned short fast_crc16(unsigned short sum, const unsigned char *p, unsigned int len)
{
    while (len--)
        sum = crc16_table[(sum >> 8) ^ *p++] ^ (sum << 8);
    return sum;
}


unsigned short slow_crc16(unsigned short sum, unsigned char *p, unsigned int len)
{
    while (len--)
    {
        int i;
        unsigned char byte = *p++;

        for (i = 0; i < 8; ++i)
        {
            unsigned long osum = sum;
            sum <<= 1;
            if (byte & 0x80)
                sum |= 1 ;
            if (osum & 0x8000)
                sum ^= 0x1021;
            byte <<= 1;
        }
    }
    return sum;
}


#if 0
extern unsigned short __checksum;
extern unsigned int __checksum_begin;
extern unsigned int __checksum_end;

bool checksum_self()
{
    unsigned short sum=0;
    
#ifdef SLOW_CRC16
    sum = slow_crc16(sum,(unsigned char *)&__checksum_begin,
                     (unsigned int)&__checksum_end -(unsigned int)&__checksum_begin +1);
    sum = slow_crc16(sum,(unsigned char *)&zero, 2);
#else
    sum = fast_crc16(sum,(unsigned char *)&__checksum_begin,
                     (unsigned int)&__checksum_end -(unsigned int)&__checksum_begin +1);
#endif

    return (sum==__checksum);
}

bool checksum_boot()
{
    unsigned short sum=0;
    unsigned int boot_begin=BOOT_BEGIN;
    unsigned int boot_end=BOOT_END;
    unsigned short checksum=*((unsigned short *)(boot_end-1));

    sum = fast_crc16(sum,(unsigned char *)boot_begin,
                     (unsigned int)boot_end -(unsigned int)boot_begin -1);

    return (sum==checksum);
}

bool checksum_download()
{
    unsigned short sum=0;

    unsigned int boot_begin=DOWNLOAD_BEGIN;
    unsigned int boot_end=DOWNLOAD_END;
    unsigned short checksum=*((unsigned short *)(boot_end-1));
    unsigned int downloadSize=DOWNLOAD_SIZE;
#if 0
    downloadSize=*((unsigned int*)DOWNLOAD_SIZE_ADDR);
    if((downloadSize>0) && (downloadSize<=DOWNLOAD_SIZE)){
        boot_end=boot_begin+downloadSize-1;
        checksum=*((unsigned short *)(boot_end-1));
    }
    else{
        return false;
    }
#endif      
    sum = fast_crc16(sum,(unsigned char *)boot_begin,
                     (unsigned int)boot_end -(unsigned int)boot_begin -1);

    return (sum==checksum);

}
#endif
